Current Storage Area Networks (SANs) are designed to carry block storage traffic over predominantly Fibre Channel standard medium and protocols. There exist several proposals for moving block storage traffic over SANs built on other networking technology such as Gigabit Ethernet, asynchronous transfer mode (ATM)/SONET, InfiniBand or other networking medium and protocols. A bridge is sometimes used to couple a network processor with a switch fabric interface. For example, a switch fabric interface is standardized by the Common Switch Interface Consortium (CSIX) and known as a CSIX switch fabric. There are many other proprietary interfaces. For example, UTOPIA 3, POS-PHY 3, SPI-3, and SPI-4 are another standards. The network processors, however, often have a different interface. These bridges or translation devices, therefore, make the necessary translations between these two protocols/mediums in order to serve the clients (host computers/servers and storage target devices). Existing bridges usually allow the connection of a single network processor interface to one switch fabric interface. Such bridges may provide some functionality with respect to ingress/egress handling, congestion management, protocol translation, and Quality of Service (QoS)-based thresholding.
Many silicon vendors offer a total solution of network processor and switch fabric that work together. However, depending on the goals of the system design, it may be desirable to mix a network processor and a switch fabric from different vendors. Often this requires glue logic between the two devices because the interfaces are not compatible.
Another issue is that some switch fabrics only have an OC-192 port granularity that makes it difficult to connect OC-48 network processors, wherein, OC-192, OC-48 refer to the bandwidth of interfaces in the telecommunications world. Normally, these interfaces are for handling Synchronous Optical NETwork/Synchronous Digital Hierarchy (SONET/SDH). There are various interfaces that meet the SONET/SDH bandwidth requirements, as mentioned above, such as POS-PHY, Utopia, CSIX, SPI, etc. Therefore, more intelligent bridges are needed to mux/demux the OC-48 to OC-192 traffic.
It is difficult to build heterogeneous SANs that are scalable using these bridges/translation devices because the bridges/translation devices usually become the bottleneck as the number of clients and the number of storage devices increase. In addition, a mixed protocol environment requires the installation of complex hardware or logic on these bridges/translation devices.